Parkinsonism is related to the destruction of dopaminergic neurons in the substantia nigra; aging also affects dopaminergic neuron functions. Since the amacrine cell layer of the retina possesses dopamine-containing neurons we believe that Parkinson's disease and aging will affect a psychophysical function that Enoch relates to amacrine cell activity. In pilot work we have found evidence of an age related decline in visual function as measured by this test. We have also found that older long-time smokers do not show this decline. We wish to study this psychophysical test in non-smoking observers from 20 to 69 years of age and to also study a special group of 60-69 year old long-time smokers. This project is health related in its study of aging and smoking and its possible relevance to a theory of the etiology of Parkinson's disease. Our method as to determine the ability to detect a slowly flashing dot surrounded by either a static or moving 'windmill' shape; amacrine cell function is supposedly measured by an inhibitory effect induced by the movement of the 'windmill'. We also wish to determine if 'critical flicker frequency' correlates with the results of the test.